1. Field of the Invention
The invention relates to false-twist textured yarns made from continuous filaments having modified cross-sections, and is more particularly concerned with polyester yarns which can be false-twist textured for use in fabrics having improved visual aesthetics.
2. Description of the Prior Art
Apparel fabrics knitted or woven from false-twist textured, continuous filament synthetic yarns are finding increasing acceptance in the trade. The texturing is needed to eliminate the undesirable slickness of fabrics made from synthetic filaments. The fabric aesthetics can be further improved by using fibers having a modified (i.e., non-round) cross-section which lead to higher bulk, a crisper and drier hand, better cover, and a pleasing subdued luster. Unfortunately, fabrics produced from false-twist textured yarns often have an undesirable glitter or sparkle, i.e., reflection of light in intense beams from tiny areas of the fabrics. Except for certain novelty applications, this glitter is highly objectionable and detracts from the appearance of the fabric, particularly when the fabric is dyed in dark shades.
A variety of methods are used to texture filaments depending on the use of the yarn. One which has met with considerable .[.commerical.]. .Iadd.commercial .Iaddend.success is false-twist texturing. In this process the yarn is twisted, heat-set in the twisted configuration as it approaches a spindle or other twist trap, and then untwisted as it released from the spindle or twist trap. The released yarn has a tendency to resume its twisted shape, thus causing the filaments to become crimped and looped, thereby creating bulk and elasticity in the yarn. Under the conditions normally used to false-twist texture yarns, i.e., with high twist levels and temperatures above the softening point, the individual filaments in the twisted hot yarn become distorted, tending to form flat surfaces with reflect light in intense beams which are observed as glitter in fabrics prepared from these yarns. It has been found that when more than about 12 percent of the filaments in a multifilament textured yarn have cross-sections with a flattened periphery greater than 10 microns in length, fabrics produced from these textured yarns will exhibit objectionable glitter. The flattening of filaments can be observed in transverse cross-sectional slices of the yarn under a microscope.
The subject of glitter in fabrics made from untextured yarns has been discussed in the prior art and means for reducing this glitter have been suggested. For example, Strachan U.S. Pat. No. 3,156,607 discloses fibers having oblong cross-sections of specified geometry which provide a combination of desirable properties including a low sparkle. One example describes the preparation of polyethylene terephthalate yarns (3 denier/filament) with a hexalobal oblong cross-section, which are crimped in a stuffing box, cut into staple and formed by conventional means into a fabric which is free from objectionable glitter. Craig U.S. Pat. No. 2,959,839 describes polyester fibers having corrugated cross-section which are formed into staple yarns and produce fabrics which are free of glitter.
Sims U.S. Pat. No. 3,425,893 discloses that the luster of trilobal filaments is improved when the lobes are substantially uniformly bent in one direction along the length of the filaments, and that better aesthetic properties are obtained in sheer fabrics with five-, seven-, and nine-lobed skewed filaments.
The problem of reducing the size of flat surface deformation sufficiently to overcome objectionable glitter is particularly serious when false-twist texturing multifilament textile yarn of polyester filaments. This problem is more easily overcome with 6--6 nylon filaments, which have better recovery from such deformation during false-twist texturing. The problem is also more easily overcome when the filaments are of low denier, but fine denier filaments provide fabrics which are generally less desirable because they are too soft and lack crispness.